Field
The present disclosure relates to an active-matrix organic light emitting display and a circuit thereof.
Discussion of the Related Art
An active-matrix organic light emitting display comprises self-luminous organic light emitting diodes OLED, and has the advantages of fast response time, high luminous efficiency, high luminance, and wide viewing angle. An organic light emitting diode, which is a self-luminous device, has the structure shown in FIG. 1. The organic light emitting diode comprises an anode and a cathode, and organic compound layers formed between the anode and the cathode. The organic compound layers comprise a hole transport layer HTL, an emission layer EML, and an electron transport layer ETL. When an operating voltage is applied to the anode and the cathode, a hole (indicated by “+” in FIG. 1) passing through the hole transport layer HTL and an electron (indicated by “−” in FIG. 1) passing through the electron transport layer ETL move to the emission layer EML, and form an exciton. As a result, the emission layer EML generates visible light.
In an organic light emitting display, pixels each comprising an organic light emitting diode are arranged in a matrix, and the luminance of the pixels is adjusted based on the grayscale of video data. Each individual pixel comprises a driving transistor that controls the driving current flowing through the organic light emitting diode based on a gate-source voltage, a capacitor that keeps the gate-source voltage of the driving transistor constant for one frame, and at least one switching transistor that programs the gate-source voltage of the driving transistor in response to a gate signal. A driving current is determined by the driving transistor's gate-source voltage corresponding to a data voltage, and the luminance of the pixel is proportional to the amount of driving current flowing through the organic light emitting diode.
Such an organic light emitting display has variations in driving current even with the same data voltage because the threshold voltage of the driving transistor varies between the pixels due to process deviation, variation of gate-bias stress with time, etc.